The current proposal is a five year competitive renewal application by the Massachusetts General Hospital to support its Mallinckrodt General Clinical Research Center (GCRC). The GCRC has served the needs of clinical investigators at the Massachusetts General Hospital for more than 70 years. It has been funded by the National Institutes of Health for thirty five years, first as a metabolic research center (NIAMD) and since 1978 as a General Clinical Research Center (NCRR). The current application requests 1,934 patient bed days (per diem research unit) and 4,244 outpatient visits. The protocols that will utilize these resources represent clinical research from 65 investigators located in 13 units and 6 departments at the MGH. The current submission continues the expansion of GCRC utilization, initiated during the previous 5 year cycle, endocrinology, diabetes and metabolism, an increasing number of protocols from Psychiatry Neurology, Infectious Diseases, Oncology, and Gerontology are included. Almost all of the protocols are investigator initiated and the majority are supported by NIH grants. The Mallinckrodt GCRC provides facilities for a broad array of clinical research activities, particularly research requiring frequent, timed collections of blood and other bodily fluids, innovative and complex diagnostic, therapeutic and physiological techniques including facilities for gene therapy, careful control of diets, and controlled sleep schedules or light environment. Many of the new protocols include patients who are generally more ill than those studied in the past. The GCRC offers expert nursing care, sophisticated dietary and biostatistical support, an expanded Core Laboratory, and other administrative support necessary to perform clinical investigation. The GCRC is very active in training physicians, nurses, dieticians, and students in clinical investigation. The educational efforts on the GCRC include post-graduate training supported through several mechanisms including CAP programs to train clinical investigators, supported by the GCRC, have been initiated. The Mallinckrodt GCRC has a long history of excellence in clinical investigation and has been the site of meaningful advances in clinical medicine for more than six decades. It will continue to serve as the major site for inpatient and outpatient clinical investigation at the MGH.